The present disclosure generally relates to heat exchangers, and more particularly relates to heat exchangers having a stack of a plurality of flat tubes that each carries a fluid through its interior, with the flat tubes being spaced apart by raised projections or dimples on the flat faces of the tubes, wherein the dimples of one tube contact the dimples of the adjacent tube so as to space the flat faces apart by twice the dimple height. In this manner, flow paths are defined between the spaced-apart flat faces for flow of another fluid so that heat exchange can take place with the fluid flowing through the interiors of the flat tubes. Typically, a fluid at a relatively high temperature is passed through the interiors of the tubes, a coolant at a lower temperature is passed through the spaces between the tubes, and heat is transferred between the fluids to cool the high-temperature fluid.
In such flat tube stacks, it is known that in addition to being useful for spacing the tubes apart, the external dimples are also effective for inducing turbulence in the fluid flowing through the spaces between the adjacent tubes. Accordingly, the dimples are also sometimes referred to as “turbulators” that induce “turbulation” in the fluid flow. Such turbulation can be beneficial for enhancing the heat transfer rate between the fluids, and can also help to prevent boiling of the fluid. Typically, the dimples are round in plan shape.
Round dimples provide moderate turbulation, but in many cases a greater degree of turbulation would be desirable.
Additionally, the top or outermost surfaces of the round dimples that contact each other are relatively small and thus do not provide much stability when stacking the tubes. Accordingly, it is not uncommon for assembly of the tube stack to be faulty because of one tube slipping relative to the adjacent tube such that the dimples “nest”, resulting in too small a spacing between the tubes. Furthermore, because of the small contact areas of the round dimples, even relatively small tolerances on the dimple locations can make it more likely that the dimples will nest. If not corrected, the resulting improper tube spacing would cause undue flow restriction in the coolant and impair proper performance of the heat exchanger.